2016-02-20 03:49:00.515417 mon.0 172.21.15.7:6789/0 145 : cluster [INF] osdmap e16: 4 osds: 4 up, 4 in
2016-02-20 03:49:00.565680 mon.0 172.21.15.7:6789/0 146 : cluster [INF] mdsmap e19: 1/1/1 up {0=a=up:replay}
2016-02-20 03:49:00.565745 mon.0 172.21.15.7:6789/0 147 : cluster [INF] pgmap v36: 32 pgs: 32 active+clean; 12393 kB data, 593 MB used, 368 GB / 372 GB avail; 0 B/s rd, 0 B/s wr, 323 op/s
2016-02-20 03:49:00.334717 mon.0 172.21.15.7:6789/0 142 : cluster [INF] pgmap v35: 32 pgs: 32 active+clean; 12393 kB data, 593 MB used, 368 GB / 372 GB avail; 354 B/s rd, 96511 B/s wr, 400 op/s
2016-02-20 03:49:00.334819 mon.0 172.21.15.7:6789/0 143 : cluster [INF] mds.0 172.21.15.7:6808/19849 up:active
2016-02-20 03:49:00.392920 mon.0 172.21.15.7:6789/0 144 : cluster [INF] mdsmap e18: 1/1/1 up {0=a-s=up:active}, 1 up:standby
2016-02-20 03:49:00.515417 mon.0 172.21.15.7:6789/0 145 : cluster [INF] osdmap e16: 4 osds: 4 up, 4 in
2016-02-20 03:49:00.565680 mon.0 172.21.15.7:6789/0 146 : cluster [INF] mdsmap e19: 1/1/1 up {0=a=up:replay}
2016-02-20 03:49:00.565745 mon.0 172.21.15.7:6789/0 147 : cluster [INF] pgmap v36: 32 pgs: 32 active+clean; 12393 kB data, 593 MB used, 368 GB / 372 GB avail; 0 B/s rd, 0 B/s wr, 323 op/s
2016-02-20 03:49:01.599201 mon.0 172.21.15.7:6789/0 150 : cluster [INF] mds.? 172.21.15.7:6809/19849 up:boot
2016-02-20 03:49:01.599342 mon.0 172.21.15.7:6789/0 151 : cluster [INF] mds.0 172.21.15.18:6808/29561 up:reconnect
2016-02-20 03:49:01.599467 mon.0 172.21.15.7:6789/0 152 : cluster [INF] mdsmap e20: 1/1/1 up {0=a=up:reconnect}, 1 up:standby
2016-02-20 03:49:01.599201 mon.0 172.21.15.7:6789/0 150 : cluster [INF] mds.? 172.21.15.7:6809/19849 up:boot
2016-02-20 03:49:01.599342 mon.0 172.21.15.7:6789/0 151 : cluster [INF] mds.0 172.21.15.18:6808/29561 up:reconnect
2016-02-20 03:49:01.599467 mon.0 172.21.15.7:6789/0 152 : cluster [INF] mdsmap e20: 1/1/1 up {0=a=up:reconnect}, 1 up:standby
there were mds takeovers even we didn't enable mds thrash.
2016-02-20 03:48:59.809408 7fd4c8036700 1 -- 172.21.15.7:6789/0 <== mds.0 172.21.15.7:6808/19849 20 ==== mdsbeacon(4179/a-s up:active seq 12 v17) v4 ==== 355+0+0 (3921659038 0 0) 0x7fd4db429c00 con 0x7fd4db7cb080
2016-02-20 03:48:59.809480 7fd4c8036700 20 mon.b@0(leader) e1 _ms_dispatch existing session 0x7fd4dba8cc40 for mds.? 172.21.15.7:6808/19849
2016-02-20 03:48:59.809489 7fd4c8036700 20 mon.b@0(leader) e1 caps allow *
2016-02-20 03:48:59.809500 7fd4c8036700 10 mon.b@0(leader).paxosservice(mdsmap 1..17) dispatch 0x7fd4db429c00 mdsbeacon(4179/a-s up:active seq 12 v17) v4 from mds.0 172.21.15.7:6808/19849 con 0x7fd4db7cb080
2016-02-20 03:48:59.809510 7fd4c8036700 5 mon.b@0(leader).paxos(paxos active c 1..124) is_readable = 1 - now=2016-02-20 03:48:59.809510 lease_expire=2016-02-20 03:49:04.074688 has v0 lc 124
2016-02-20 03:48:59.809526 7fd4c8036700 10 mon.b@0(leader).mds e17 preprocess_query mdsbeacon(4179/a-s up:active seq 12 v17) v4 from mds.0 172.21.15.7:6808/19849
2016-02-20 03:48:59.809541 7fd4c8036700 20 is_capable service=mds command= exec on cap allow *
2016-02-20 03:48:59.809545 7fd4c8036700 20 allow so far , doing grant allow *
2016-02-20 03:48:59.809546 7fd4c8036700 20 allow all
2016-02-20 03:48:59.809548 7fd4c8036700 12 mon.b@0(leader).mds e17 preprocess_beacon mdsbeacon(4179/a-s up:active seq 12 v17) v4 from mds.0 172.21.15.7:6808/19849 compat={},rocompat={},incompat={1=base v0.20,2=client writeable ranges,3=default file layouts on dirs,4=dir inode in separate object,5=mds uses versioned encoding,6=dirfrag is stored in omap,8=no anchor table}
2016-02-20 03:48:59.809562 7fd4c8036700 20 mon.b@0(leader).mds e17 preprocess_beacon health metrics for gid 4179 were updated
2016-02-20 03:49:00.334984 7fd4c9839700 10 mon.b@0(leader).mds e18 e18: 1/1/1 up {0=a-s=up:active}, 1 up:standby
2016-02-20 03:49:00.335006 7fd4c9839700 10 mon.b@0(leader).mds e18 no beacon from 4179 172.21.15.7:6808/19849 mds.0.2 up:active since 2016-02-20 03:48:43.808993
2016-02-20 03:49:00.335022 7fd4c9839700 10 mon.b@0(leader).mds e18 replacing 4179 172.21.15.7:6808/19849 mds.0.2 up:active with 4136/a 172.21.15.18:6808/29561
looks like monitor does note beacon if health metrics changes.
https://github.com/ceph/ceph/pull/7757